Modern communication devices, such as 802.x enabled communication devices, may utilize a conventional transceiver to transmit and/or receive signals with variable signal strength. One or more voltage controlled oscillator (VCO) circuits may be utilized within the conventional transceiver to generate oscillator reference signals with a specific output frequency and/or phase. The generated oscillator reference signals may then be utilized by a transmitter and/or by a receiver within the 802.x enabled device to facilitate processing of a received signal and/or processing of a signal prior to transmission. A phase frequency detector may also be utilized in a phase locked loop (PLL) for controlling the VCO to generate an output signal with desired frequency.
The voltage controlled oscillator circuits within the conventional transceiver may be adapted to generate one or more differential frequency output signals. Outputs of these voltage controlled oscillator circuits may be coupled to one or more divider circuits, for example, that divide the generated differential frequency output signals for subsequent use by other circuits within the transceiver. The voltage controlled oscillators, however, are sensitive to loading from these divider circuits and/or from other interconnections. Large capacitance from loading and/or resistance created by divider circuits and line routing may decrease the quality factor and limit performance of the voltage controlled oscillator circuits within the transceiver.
In this regard, the desired output frequency of the differential output signal generated by the voltage controlled oscillator may change and re-calibration may be required. In addition, variations caused by environmental factors and PTV may result in deviations in the desired output frequency of the differential output signals generated the VCO circuits. Consequently, a phase locked loop (PLL) may be required to control the VCO to generate output differential signals with desired output frequency.
Within the PLL, a phase frequency detector may be utilized to detect a phase and/or frequency difference between a reference signal and a voltage controlled oscillator output signal. Conventional phase frequency detectors, however, are characterized by increased overlapping time between up and down output signals of the phase frequency detector, which increases charge pump phase noise contribution and reference signal feedthrough in the voltage controlled oscillator output signal. An up output signal of the phase frequency detector may be generated when a first input signal leads a second input signals. For example, an up output signal may be generated when a reference input signal leads a VCO input signal. Similarly, a down output signal may be generated by the phase frequency detector when the reference input signal lags the VCO input signal.
In some instances, conventional phase frequency detectors are characterized by reduced overlapping time between the up and down output signals of the phase frequency detector. Consequently, “dead zone” effects significantly increase because of the reduced overlapping time, resulting in increase in phase noise in the voltage controlled oscillator differential output signals.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.